Re: [Qemu-devel] [RFC] Memory API

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/18/2011 10:23 AM, Avi Kivity wrote:
>> The tricky part is wiring this up efficiently for TCG, ie. in QEMU's
>> softmmu. I played with passing the issuing CPUState (or NULL for
>> devices) down the MMIO handler chain. Not totally beautiful as
>> decentralized dispatching was still required, but at least only
>> moderately invasive. Maybe your API allows for cleaning up the
>> management and dispatching part, need to rethink...
>
> My suggestion is opposite - have a different MemoryRegion for each (e.g.
> CPUState::memory). Then the TLBs will resolve to a different ram_addr_t
> for the same physical address, for the local APIC range.

I don't understand the different ram_addr_t part.

The TLB should dispatch to a per-CPU dispatch table.  The per-CPU should 
dispatch almost everything to a global dispatch table.

The global dispatch table is the chipset (Northbridge/Southbridge).

The chipset can then dispatch to individual busses which can then 
further dispatch as appropriate.

Overlapping regions can be handled differently at each level.  For 
instance, if a PCI device registers an IO region to the same location as 
the APIC, the APIC always wins because the PCI bus will never see the 
access.

You cannot do this properly with a single dispatch table because the 
behavior depends on where in the hierarchy the I/O is being handled.

Regards,

Anthony Liguori